Add answers for lab3 part A
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answers-lab3.txt
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answers-lab3.txt
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1. Some interrupts receive a different "shape" of stack frame - the kernel pushes
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an error code for some, but not for the others. We thus need individual handlers
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that would make sure that what we have on the stack is consistent, and
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then call one centralized function for that. The handlers additionally
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are able to pass in a trap number to that centrallized function. This way, a lot
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of code can be re-used.
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Conceptually, each trap has a different semantic meaning. Thus, it makes no sense
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to perform the same action for both traps - they don't mean the same thing.
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2. The general protection fault occurs when a process can access memory, but not do something else with it. We do not want page faults to be trigger-able by users (this is the case for many other traps). Thus, when the user tries to invoke int 14,
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it's not allowed to execute it from userspace, so it is thrown a general protection fault, which it then prints.
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